So I bought a one month old Jayco Eagle HT last summer that has three slides. I used it from August until December last season with zero issues in all kinds of weather. After this kind of investment ...
I've seen where Jayco builds their slide roofs on some units sloping in towards the sides of the coach instead of towards the outside. If you have a leaky seal then all the water on the slide roof will run towards the coach vs to the outer edge of the slide.